The Russian Navy reports of an accident on a nuclear submarine deployed in the Pacific, which took place today, on November 8, 2008. According to the Navy, the submarine was at sea undergoing sea trials when the fire control system accidentally switched on killing "more than 20 people" of the 208 people on board. Among the killed are members of the crew as well as representatives of a shipyard (presence of the shipyard workers explains the large number of people on board - normal crew size is 73 people). The reactors as well as other vital systems of the submarine were not affected and the submarine is returning "to its temporary base".
The type of the submarine is not known at this point. It is fairly certain that this is not a ballistic missile submarine. It may be one of the attack submarines of the Project 971 class - as one report points out, it was reported in October that a submarine of this class was undergoing sea trials in the Pacific.
UPDATE: One important note - the submarine almost certainly does not have any nuclear weapons on board. First, it wouldn't carry them during sea trials. Then, Russian submarines (other than ballistic missile submarines) do not carry nuclear weapons.
UPDATE: It was indeed a Project 971 submarine. This boat, K-152, was built at the Komsomolsk-na-Amure shipyard for the Indian Navy.